Covering material for solar thermal power generating system and solar thermal power generating system formed by spreading the covering material

ABSTRACT

A covering material for solar thermal power generation system, characterized in that it is made of a film which has a tensile yield strength of at least 10 N/mm 2  according to JIS K7127, a solar radiation transmittance of at least 85% according to JIS R3106, and a retention of at least 80% against the initial value of the tensile breakage strength after 5000 hours of the sunshine carbon arc lamp weather test according to JIS B7753.

This is a continuation application of U.S. application Ser. No.11/344,116, filed Feb. 1, 2006, which is a continuation ofPCT/JP04/10942 filed on Jul. 30, 2004.

TECHNICAL FIELD

The present invention relates to a covering material for solar thermalpower generating system and a solar thermal power generating systemformed by spreading the covering material. In more detail, the presentinvention relates to a covering material for solar thermal powergenerating system, which is excellent in mechanical strength,transparency and weather-resistance, and to a solar thermal powergenerating system formed by spreading the covering material.

BACKGROUND ART

In recent years, power generating methods for generating clean andrenewable energy have been progressed to cope with fear of exhaustion ofoil energy and environmental problem. As representative examples, windpower generation and solar-light-condensing power generation arementioned. Wind power generation has already been practically used inEurope and Asia, but it has a problem that power-generation quantitysignificantly decreases when wind speed decreases. Further, in the solarlight-condensing power generation which is a method of condensing solarlight by using a parabolic mirror to obtain solar energy and using thesolar energy to produce high-temperature vapor for driving a powergenerator. However, it has a problem that sufficient solar energy cannot be obtained when sun light is prevented by cloud.

Recently as a new power generation method, a power generating systemusing solar energy called solar chimney has been proposed (for example,Non-Patent Document 1). This power generating system using solar energyhas a construction comprising a circular heat collector having adiameter of 4 km and having a chimney of 1 km high in the center. Theheat collector has a structure like a greenhouse having no peripheralwall. The heat collector is configured so that air heated in the heatcollector moves inside a roof of the heat collector towards the centerto which the slope is sloping up, and reaches the highest point at thecenter. The heated air is drawn into the chimney disposed at the centerof the heat collector. At this time, a wind-power generating turbinedisposed in the chimney generates electric power. Since the temperaturein the heat collector is higher than the outside temperature in thesolar chimney system, air flow is generated by the heated air in theheat collector and power-generation is continued even if sun light isprevented by cloud. Further, by disposing a heat accumulator in the heatcollector, power-generation is possible even in night time by heatingair by heat irradiation from the heat accumulator.

Further, in a solar light-condensing power generation, instead of aconventional method of condensing solar light into one point by aparabolic mirror, an improved solar light-condensing power generationmethod is proposed (for example, refer to Patent Document 1), accordingto which a curved rectangular mirror is used to condense solar lightinto a linear shape to produce a large quantity of high-temperaturevapor at one time.

Non-Patent Document 1 describes that a vinyl resin can be used as acovering material to be used for a solar thermal power generationsystem. In a case where a material having insufficientweather-resistance is used as a covering material for a heat collectorof a solar chimney which is intended to supply electric power almostpermanently, periodic replacement is required and cost for such areplacing work of a roof of the heat collector having a large area,becomes high. As a result, there is a problem that power-generation costis increased. Further, the wind pressure of air heated in the heatcollector increases as the air moves toward the center. Therefore, whena material having insufficient mechanical strength is employed,support-structures have to be installed at a small interval, whichcauses a problem that solar light is blocked by such support-structuresto reduce power-generation efficiency. On the other hand, in a casewhere a glass excellent in weather-resistance and mechanical strength,is employed, thick support-structures have to be provided at a smallinterval to support the weight of the glass, which causes a problem thatsolar light is blocked to reduce power-generation efficiency.

Therefore, in a solar thermal power generation system, development of acovering material excellent in mechanical strength, weather resistanceand transparency, has been desired.

Patent Document 1: JP-A-2002-115917

Non-Patent Document 1: NEDO International Report No. 869 (published onNov. 19, 2001)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

It is an object of the present invention to provide a covering materialfor solar thermal power generation system, excellent in mechanicalstrength, transparency and weather resistance and excellent in workingefficiency of covering a large-area heat collector, and to provide asolar thermal power generation system formed by spreading the coveringmaterial.

Means for Solving the Problems

The present invention provides a covering material for solar thermalpower generation system, characterized in that it is made of a filmwhich has a tensile yield strength of at least 10 N/mm² according to JISK7127, a solar radiation transmittance of at least 85% according to JISR3106, and a retention of at least 80% against the initial value of thetensile breakage strength after 5000 hours of the sunshine carbon arclamp weather test according to JIS B7753.

Further, the present invention provides a solar thermal power generationsystem formed by spreading the covering material for solar thermal powergeneration system.

EFFECT OF THE INVENTION

The covering material for solar thermal power generation system of thepresent invention, has high tensile yield strength enabling to widen theinterval of support-structures in the heat collector, and the coveringmaterial is excellent in transparency and provides excellentpower-generation efficiency. Further, since the material is excellent inweather-resistance, it is not necessary to be replaced for a long time,which reduces maintenance cost. Further, by employing a wide-width filmobtained by fusion-bonding, the heat collector can be coveredefficiently. Further, by attaching a cable at the end of the film, theheat collector can be covered efficiently and easily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: A schematic cross-sectional view showing an example of a solarthermal power generation system according to the present invention.

FIG. 2: Cross-sectional views (A), (B) and (C) each showing an exampleof fusion-bonded portion of films

FIG. 3: A cross-sectional view showing an example of an end of a film towhich a cable is attached.

FIG. 4: Cross-sectional views (A), (B) and (C) each showing an exampleof connecting jig.

FIG. 5: Cross-sectional views (A) and (B) each showing an example ofconnecting portion.

FIG. 6: A partial perspective view showing an example of a heatcollector of a solar thermal power generation system.

EXPLANATION OF NUMERALS

-   -   1 Solar thermal power generation system    -   10 Chimney    -   20 Heat collector    -   21 Peripheral portion of heat collector    -   22 Center of heat collector    -   30 Power generator    -   201 Film    -   202, 203 and 205 Fusion-bonded portion    -   204 and 206 Reinforcement film    -   207 Cable    -   208 Fusion-bonded portion at the end of film    -   209, 210 and 211 Connecting jig    -   212 C-shaped pipe    -   213 Pipe for reinforcement wire    -   214 Ring for letting tension wire through    -   220 Reinforcement wire    -   221 Tension wire    -   230 and 231 Connecting portion    -   240 Pole    -   241 Support-structure to which a connecting jig is attached

BEST MODE FOR CARRYING OUT THE INVENTION

A film of the covering material for solar thermal power generationsystem of the present invention, has a tensile yield strength of atleast 10 N/mm² according to JIS K7127, a solar radiation transmittanceof at least 85% according to JIS R3106, and a retention of at least 80%against the initial value of the tensile breakage strength after 5000hours of the sunshine carbon arc lamp weather test according to JISB7753.

The film of the present invention has a tensile yield strength of atleast 10 N/mm² according to JIS K7127. It is preferably at least 15N/mm². When the film has a tensile yield strength of at least 10 N/mm²,it is excellent in durability against wind pressure, which enables toreduce the number of support-structures to widen the interval of thesupport-structures. As a result, the number of support-structures can bereduced and cost can be reduced. Further, since sun light is less likelyto be blocked by the support-structures, utilization efficiency of sunlight can be increased and power-generation efficiency can be increased.The tensile yield strength is preferably as strong as possible. Usually,the upper limit of the tensile yield strength is 250 N/mm².

The film of the present invention has a solar radiation transmittance ofat least 80% according to JIS R3106. The solar radiation transmittanceis an index of transmittance for solar light consisting of UV light,visible light and near infrared light. The higher the index is, the moreexcellent in transmittance is. The solar radiation transmittance ispreferably at least 85%, more preferably at least 90%. The solarradiation transmittance is theoretically at most 100%.

Further, the film has a transmittance for a radiation of 10 μmwavelength as a transmittance for infrared radiation, of preferably atmost 50%, more preferably at most 30%, the most preferably at most 10%.The lower the transmittance for infrared radiation is, the less theinfrared rays are radiated. When the transmittance for radiation of 10μm wavelength, is within this range, little heat accumulated in the heatcollector is radiated to the outside in nighttime, and thus the film issuitable for power generation of nighttime. The transmittance ofinfrared radiation is theoretically at least 0%.

The film of the present invention has a retention of at least 80%against the initial value of the tensile breakage strength after 5,000hours of the sunshine carbon arch lamp weather test according to JISB7753. More preferably, it has the retention of at least 85%. Theretention is theoretically at most 100%. 5,000 Hours of the sunshinecarbon arc lamp weather test, is said to be correspond to 10 years ofactual exposure test in outdoors. Therefore, if the retention is withinthis range, the film is excellent in weather-resistance, the film isusable for a long time without replacement, and thus the film issuitable for solar thermal power generation system which is intended forpermanent operation.

The thickness of the film of the present invention is preferably from 1to 1,000 μm, more preferably from 10 to 500 μm, still more preferablyfrom 50 to 300 μm.

The material to be employed for the film of the present invention, may,for example, be a fluororesin such as an ethylene tetrafluoroethylenetype copolymer (ETFE), a tetrafluoroethylene-perfluoroalkyl vinyl ethercopolymer (PFA), a tetrafluoroethylene-hexafluoropropylene copolymer(FEP), a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoridecopolymer (THV), polyvinylidene fluoride (PVdF) or polyvinyl fluoride(PVF), an acrylic resin such as polymethyl acrylate or anethylene-methyl acrylate type copolymer, a methacryl resin such aspolymethyl methacrylate, polyethyl methacrylate or anethylene-methacrylate copolymer, a polyester resin such as polyethyleneterephthalate or polybutylene terephthalate, or a polycarbonate resin.

The material is preferably at least one member selected from the groupconsisting of ETFE, PFA, FEP, THV, PVdF and PVF. More preferably, it isat least one member selected from the group consisting of ETFE, FEP andPVF, most preferably ETFE. ETFE is excellent in tensile yield strength,solar radiation transmittance and weather resistance.

The ETFE in the present invention is preferably a copolymer oftetrafluoroethylene and ethylene, or a copolymer of tetrafluoroethylene,ethylene and another monomer.

Above another monomer may, for example, be a fluoroolefin such aschlorotrifluoroethylene, hexafluoropropylene (HFP), perfluoro(alkylvinyl ether) (PFAV) or vinylidene fluoride; a polyfluoroalkylethylenesuch as CH₂═CHR^(f) (hereinafter, R^(f) indicates a polyfluoroalkylgroup having a carbon number of 1 to 8.) or CH₂═CFR^(f); or apolyfluoroalkyl trifluorovinyl ether such as CF₂═CFOCH₂R^(f). These maybe used alone or used in combination of at least two types.

Above another monomer is preferably at least one member selected fromthe group consisting of HFP, PFAV, CH₂═CHR^(f) and CH₂═CFR^(f). The PFAVis preferably CF₂═CFOR^(f), wherein R^(f) is more preferablyperfluoroalkyl group having a carbon number of 3 to 6, the mostpreferably C₃F₇. R^(f) in CH₂═CHR^(f), is more preferably aperfluoroalkyl group having a carbon number of 3 to 6, most preferablyC₄F₉. R^(f) in CH₂═CFR^(f), is more preferably a perfluoroalkyl grouphaving a carbon number of 3 to 6, most preferably C₃F₇. The aboveanother monomer is most preferably CH₂═CHR^(f).

In terms of the composition of the ETFE, the molar ratio of “monomerunits based on tetrafluoroethylene”/“monomer units based on ethylene”,is preferably from 70/30 to 30/70, more preferably from 65/35 to 40/60,most preferably from 60/40 to 45/55.

In a case where monomer units based on another comonomer are contained,the content of the monomer units based on another comonomer, ispreferably from 0.01 to 30 mol %, more preferably from 0.05 to 15 mol %,the most preferably from 0.1 to 10 mol %, based on the sum of the molesof the monomer units based on tetrafluoroethylene and the moles of themonomer units based on ethylene.

The film of the present invention is preferably a film having onesurface subjected to a hydrophilic treatment. Particularly, in a casewhere the film has inner surface subjected to hydrophilic treatment, thesurface is excellent in dripping property and accordingly, waterdroplets are unlikely to be present inside of the covering material evenif dew-condensation occurs. By this effect, sunlight blockage by thewater droplets is reduced and the film is excellent in power-generationefficiency. As the method for forming a hydrophilic-treatment surface, awet method or a dry method is used. As the wet method, a method ofcoating with a solution of hydrophilic material by a roller, a method ofspraying such a solution, a method of applying such a solution by abrush, a method of coating with such a solution by a coater, or the likemay be mentioned. The wet method is preferably a method of coating witha solution of hydrophilic material by a coater, or a method of sprayingsuch a solution.

As the dry method, a sputtering method, a vacuum vapor depositionmethod, a CVD (Chemical Vapor Deposition) method or an ion-platingmethod of a hydrophilic material, may be mentioned. The dry method ispreferably a sputtering of hydrophilic material, which has highproductivity and excellent in durability of hydrophilic property.

As the hydrophilic material, an inorganic colloid sol of e.g. SiO₂ orAl₂O₃, a hydrophilic resin of e.g. polyvinyl alcohol or acrylic acid, ametal oxide of e.g. Si, Sn, Ti, Nb, Al or Zn, may be mentioned. Inparticular, a sputtering of a metal oxide of e.g. Si, Sn or Ti, ispreferred. In this case, a metal oxide of Si or Ti is more preferablyemployed.

When the film of the present invention has a hydrophilic treatmentsurface, it is preferred that the underside of the roof of the heatcollector of the solar thermal power generation system is thehydrophilic-treatment surface.

From now, the present invention will be described with reference todrawings. However, the present invention is not limited to these.

FIG. 1 is a schematic cross-sectional view showing an example of thesolar thermal power generation system according to the presentinvention. A solar thermal power generation system 1 comprises a chimney10, a heat collector 20 and a power generator 30. The heat collector 20has a roof 215 including a film 201. The roof 215 has a continuous slopesloping up from the periphery 21 of the heat collector towards thecentral portion 22 of the heat collector. Solar light heats up airinside the heat collector 20. Heated air moves along the roof 215 of theheat collector 20 towards the center 22 of the heat collector. Namely,the air moves from the outer periphery 21 of the heat collector towardsthe center 22 of the heat collector as it is heated. The heated air issucked into the chimney 10 at the center 22 of the heat collector, andthe air is discharged from the top of the chimney 10. A wind-powergeneration turbine is disposed in the power generator 30 in the vicinityof the center 22 of the heat collector. When the heated air moves fromthe heat collector 20 to the chimney 10, the wind power generationturbine is rotated to generate electricity.

The diameter of the heat collector in the solar thermal power generationsystem, is preferably from 100 to 8,000 m, more preferably from 800 to5,000 m. The height of the chimney 10 is preferably from 100 to 2,000 m,more preferably from 200 to 1,500 m. Further, the diameter of thechimney is preferably from 5 to 300 m, more preferably from 10 to 200 m.

The film of the present invention is preferably a film having a largewidth formed by fusion bonding ends of plural films. Such a film havinga large width can efficiently cover the heat collector. As a method forfusion bonding, a thermal fusion bonding, an ultrasonic fusion bonding,a high-frequency fusion bonding or the like may be mentioned. A thermalfusion bonding is preferred since it forms fusion bonded portions havinghigh strength and it is excellent in productivity.

FIG. 2 includes cross-sectional views (A), (B) and (C) showing examplesof fusion-bonded portions of films. Namely, they are cross-sectionalviews respectively showing three examples of fusion-bonded structures atfusion-bonded portions of two films. The fusion-bonded portion of filmsshown in FIG. 2(A) being a fusion-bonded portion view, is formed byoverlapping ends of two films 201 and fusion bonding the overlappedportion. The fusion-bonded portion of films shown in FIG. 2(B), isformed by overlapping ends of two films 201, overlaying a reinforcementfilm 204 on the overlapped portion, and fusion bonding the portion. Thefusion-bonded portion of films shown in FIG. 2(C), is formed by placingends of two films 201 close to each other, overlapping a reinforcementfilm 206 on such a portion where the ends are placed closely to eachother, and fusion bonding the portion.

The width of each overlapped portion in the fusion-bonded portion ofFIG. 2(A) and fusion-bonded portion of FIG. 2(B), is preferably from 1to 200 mm, more preferably from 3 to 100 mm, still more preferably from5 to 60 mm. The width of each of the reinforcement film 204 and thereinforcement film 206 is preferably from 5 to 250 mm, more preferablyfrom 10 to 100 mm, still more preferably from 15 to 70 mm.

The film of the present invention is preferably a film having a cableattached to its end. When a film has a cable attached to its end, theheat collector can be efficiently and easily covered with the film byinserting the cable into a connecting jig attached to asupport-structure. The method for attaching the cable to the end ispreferably a method of folding the periphery of the film, enclosing thecable in the folded periphery and thermally fusion-bonding the surfacesof the folded periphery to each other.

FIG. 3 is a cross-sectional view showing an example of an end of a filmto which a cable is attached. A cable 207 is placed on an end of a film201. The end of the film is folded to enclose the cable. The overlappingportion of the folded end of the film 201 and a portion of the film 201in contact with the folded end, namely film surfaces of thefusion-bonded portion 208, are thermal-fusion-bonded. By this process,the end of the film 201 to which the cable 207 is attached, is formed.The cable may, for example, be a resin cable, a resin-coated metal cableor a metal cable. A resin cable is preferred since it unlikelymechanically damage the film. Among resin cables, a polyvinyl alcoholresin cable is more preferred. The diameter of the cable is preferably 2to 50 mm, more preferably 5 to 30 mm. When one side of the film 201 issubjected to a hydrophilic treatment, it is preferred thatnon-hydrophilic treatment surfaces are fusion bonded to each other. Whennon-hydrophilic-treated surfaces are fusion-bonded to each other,strength of the fusion-bonded portion increases and the fusion-bondedportion becomes less likely to be peeled off, such being preferred.

The connecting jig is preferably a jig having a shape formed byconnecting the backs of C-shaped pipes each having a slit and having aC-shaped cross section.

FIG. 4 includes cross-sectional views (A), (B) and (C) each showing anexample of connecting jig. The connecting jig 209 shown in FIG. 4(A),has a shape formed by linearly connecting a C-shaped pipe 212, a pipe213 for reinforcement wire, and a C-shaped pipe 212. The connecting jig210 shown in FIG. 4(B), has a shape formed by connecting a C-shaped pipe212, a pipe 213 for reinforcement wire, and a C-shaped pipe 212, inV-shape, wherein a ring 214 for letting a tension wire through isattached to the pipe 213 for reinforcement wire. The connecting jig 211shown in FIG. 4(C) has a shape formed by connecting two C-shaped pipes212 without intervention of a pipe for reinforcement wire. Theconnecting jig may have the pipe 213 for reinforcement wire but do nothave to have the pipe. The connecting jig preferably has the pipe 213for reinforcement wire since the rigidity of the connecting jig can beincreased by letting a wire through the pipe 213 for reinforcement wire.The slit width L of the C-shaped pipe 212 is larger than the thicknessof the film 201 but smaller than the diameter of the cable. L ispreferably from 5 to 90%, more preferably from 30 to 80%, of thediameter of the cable. The material of the connecting jig may, forexample, be a resin, a fiber-reinforced resin or a metal. The materialis preferably a metal, and among these, aluminum is the most preferable.

FIG. 5 includes cross-sectional views (A) and (B) showing examples ofthe connecting portion. Ends of two films 201, to which the respectivecables 207 are attached, are fit into the respective two C-shaped pipes212 of the connecting jig 209 respectively, whereby the two films areconnected to each other via the connecting jig 209. By letting areinforcement wire 220 through a pipe 213 for reinforcement wire, therigidity of the connecting jig 209 is increased. In the connectingportion shown in FIG. 5(B), Ends of two films 201, to which therespective cables 207 are attached, are fit into the respective twoC-shaped pipes 212 of the connecting jig 210, whereby the two films areconnected to each other via the connecting jig 210. By letting areinforcement wire 220 through a pipe 213 for reinforcement wire, therigidity of the connecting jig 210 is increased. By letting a tensionwire 221 through a ring 214 for letting the tension wire through, thetension wire 221 is pulled downwardly, whereby the film 201 is extended.

Each of the reinforcement wire 220 and the tension wire 221 may, forexample, be a resin wire, a resin-coated metal wire or a metal wire. Ametal wire is preferred since it has high rigidity. The diameter of thereinforcement wire 220 is preferably from 2 to 50 mm, more preferablyfrom 5 to 30 mm. The diameter of the tension wire 221 is preferably from2 to 50 mm, more preferably from 5 to 30 mm.

FIG. 6 is a partial perspective view showing an example of a heatcollector of a solar thermal power generation system. Poles 240 areerected and disposed on a ground at a predetermined interval. A roof 215formed by connecting plural films 201 by connecting jigs 209 andconnecting jigs 210, is placed on the top side of poles 240. Each of theconnecting jigs 209 of the roof 215 is attached to a support-structuralmember 241. The support-structural member 241 to which the connectingjig 209 is attached, is placed on the poles 240 so that the top ends ofthe poles 240 butt the support-structural member 241. A tension wire 221is let through a ring 214 for letting the tension wire through, of eachof the connecting jig 210. The end of the tension wire 221 is disposedat a lower part of the pole 240. By pulling the connecting jig 210 bythe tension wire 221 downwardly, the roof 215 is extended to form a heatcollector 20. In the heat collector 20, a heat-absorber such as awater-accumulating pipe may be provided. By providing such a heatabsorber, the power-generation efficiency of solar thermal powergeneration system is further increased. Further, it is possible to warmup air inside of the heat-absorber 20 by a heat radiation from the heatabsorber, to generate electricity.

The covering material for solar thermal power generation system of thepresent invention, is constituted by a film excellent in mechanicalstrength, transparency and weather resistance, and accordingly, it isusable also for greenhouses for facility cultivation, livestock house,compost houses, simple warehouses, atriums, arcades, gymnasiums,pavilions for exhibition, botanic gardens, carports, swimming pools andthe like as the application other than a solar thermal power generationsystem.

EXAMPLES

From now, the present invention will be described in detail withreference to Examples. However, the present invention is not limited tothese Examples.

Evaluation Method of Film

Tensile yield strength, solar radiation transmittance and retention oftensile breaking strength are measured by the following methods.

Tensile yield strength (n/mm²)

This is measured according to JIS K7127. Specifically, a test sample of20 mm wide×50 mm long is prepared from a film by using a razor, and atensile test is carried out at a tensile test speed of 5 mm/min by usinga tensile tester (manufactured by Toyo Baldwin Co., Ltd., LargeTensilon). The first bending point in a tensile stress-strain curverecorded in a recorder, is defined as a yield load, and a tensile yieldstrength T was calculated from the following formula (1).

T=P/S  (1)

T (N/mm²): tensile yield strength, P (N): yield load, S (mm²):cross-sectional area of test sample

Solar Radiation Transmittance (%)

This is measured according to JIS R3106. Specifically, a test sample of50 mm square was prepared from a film by using a razor, and itstransmittance within a wavelength range of from 340 nm to 1,800 nm wasmeasured by using a UV-visual spectrophotometer (manufactured byShimadzu Corporation, UV3100PC), and a solar radiation transmittance wascalculated using the weighting coefficients and the formula described inappendix table 2 of JIS R3106.

Retention (%) of Tensile Breaking Strength

A sunshine carbon arc lamp type weather-resistance test according to JISB7753 was carried out for 5,000 hours. The tensile breaking strengths ofthe film before and after the test were measured according to JIS K7127.From the tensile breaking strengths before and after the test, theretention M was calculated from the following formula (2). As theretention M is higher, the sample is more excellent inweather-resistance.

M=(Q/R)×100  (2)

M (%): retention of tensile breaking strength, Q (N): tensile breakingstrength after the test, R(N): tensile breaking strength before the test

Example 1 Example of Preparing a Film

ETFE was prepared by a solution polymerization method described inJP-A-6-157616. The copolymerization composition of the ETFE, was thatmonomer units based on tetrafluoroethylene/monomer units based onethylene/monomer units based on CH₂═CHC₄F₉=52.4/46.4/1.2 (molar ratio).The ETFE was molded by using a melt extruder with a T-shaped die, at adie-temperature of 300° C. to produce a film of 100 μm in thickness. Thetensile yield strength, the solar radiation transmittance and theweather resistance of the ETFE film obtained, were measured. The resultsare shown in Table 1.

COMPARATIVE EXAMPLES 1 and 2 Films of Comparative Examples

The same measurements as those of Example 1 were carried out withrespect to a polyvinyl chloride film (Nobi-Ace, a tradename,manufactured by Mitsubishi Chemical MKV Company, 100 μm thick), apolyethylene film (AGRISTAR, a tradename, manufactured by MitsubishiChemical MKV Company, 100 μm thick). The results are shown in Table 1.

TABLE 1 Comp. Comp. Ex. 1 Ex. 1 Ex. 2 Film ETFE PVC PE Thickness (μm)100 100 100 Tensile yield strength 15 No yield 8 T (N/mm²) point Solarradiation 94 93 88 transmittance (%) Retention M (weather 90 0 30resistance) (%)

Example 2 Example of preparing a wide film

Two ETFE films having a width of 130 cm obtained by Example 1, werefusion bonded at a fusion-bonding temperature of 260° C. by using athermal fusion bonder (manufactured by Queen Light Electronic IndustriesLtd., Heat Sealer LHP-W705). This step was repeated to produce alarge-width film having a width of 5 m. An ETFE film A was obtained bysimply overlapping and fusion bonding portions within 3 cm from the endsof films (fusion-bonded portion of FIG. 2(A)). An ETFE film B wasobtained by overlapping portions within 1 cm from the ends of films, andfurther overlapping a reinforcement film of 3.5 cm wide on theoverlapping portion (the fusion-bonded portion of FIG. 2(B)). An ETFEfilm C was obtained by butting the ends of films, overlapping areinforcement film of 3.5 cm wide on the batted portion so as to bridgethe butted portion, and fusion bonding the portion (fusion-bondedportion of FIG. 2(C)). Cross sections of the fusion-bonded portions ofthese ETFE film A1, ETFE film A2 and ETFE film A3, were shown in FIG. 2.

Example 3 Construction of a solar thermal power generation system

A cable (PVA cable) made of polyvinyl alcohol resin having a diameter of1 cm was attached to the end of a ETFE film. Specifically, theperipheral portion of the ETFE film was folded so as to wrap the PVAcable to accommodate the PVA cable. Surfaces of the peripheral portionof the ETFE film folded in a loop shape were fusion-bonded to fix thePVA cable to the end of the film, to prepare a ETFE film having a PVAcable attached to its end. The cross section of the end of the ETFE filmhaving a PVA cable attached to its end, is shown in FIG. 3. Then, usinga connecting jigs, the ETFE film having a PVA cable attached to its end,was inserted into a connecting jig 209 and a connecting jig 210. Theconnecting jig 209 is fixed to a support-structural member, and the ETFEfilm covers the support-structural member and poles. A tension wire islet through a ring for letting tension wire, of the connecting jig 210.By pulling the connecting jig downwardly by the tension wire and fixingthe end of the wire to a lower portion of the pole, the roof is extendedto form a heat collector. Further, chimney is formed and a wind powergeneration turbine was installed around the center of the heat collectorto form a power generation unit, whereby a solar thermal powergeneration system is constructed. Cross sections of the connecting jig209 and a connecting jig 210 are shown in FIG. 4, and the cross sectionof a connecting jig to which a ETFE film having a PVA cable attached toits end, is fitted, is shown in FIG. 5, and a perspective view of asupport-structural member and poles covered with the film, namely aperspective view of the heat collector, is shown in FIG. 6.

From Table 1, it is understandable that the ETFE film is excellent intensile yield strength, solar radiation transmittance and weatherresistance, and is therefore excellent as a covering material for solarthermal power generation system. Further, by repeating thefusion-bonding of the cross sectional structure of FIG. 2, a wide widthfilm can be easily obtained. As shown in FIG. 3 and FIG. 4, by using afilm having a PVA cable attached to its end, and a connecting jig, andby using a covering method shown in FIG. 5, it is possible to cover theheat collector of a solar thermal power generation system effectivelyand easily.

INDUSTRIAL APPLICABILITY

The covering material for solar thermal power generation system of thepresent invention is constituted by a film excellent in mechanicalstrength, transparency and weather-resistance, whereby it is extremelyuseful as a covering material for solar thermal power generation systemwhich can be used for a long time and excellent in utilizationefficiency of solar light.

The entire disclosure of Japanese Patent Application No. 2003-285227filed on Aug. 1, 2003 including specification, claims and summary isincorporated herein by reference in its entirety.

1. A covering material for solar thermal power generation system,characterized in that it is made of a film which has a tensile yieldstrength of at least 10 N/mm² according to JIS K7127, a solar radiationtransmittance of at least 85% according to JIS R3106, and a retention ofat least 80% against the initial value of the tensile breakage strengthafter 5000 hours of the sunshine carbon arc lamp weather test accordingto JIS B7753, wherein the film is a wide-width film formed byfusion-bonding ends of a plurality of films.
 2. The covering materialfor solar thermal power generation system according to claim 1, whereinthe film is made of at least one member selected from the groupconsisting of an ethylene/tetrafluoroethylene copolymer, atetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, atetrafluoroethylene/hexafluoropropylene copolymer, atetrafluoroethylene/hexafluoropropylene/vinylidene fluoride copolymer, apolyvinylidene fluoride and a polyvinyl fluoride.
 3. The coveringmaterial for solar thermal power generation system according to claim 1,wherein the film is a film having a hydrophilic treated surface on oneside.
 4. The covering material for solar thermal power generation systemaccording to claim 1, wherein the film is a film having a cable attachedto its end.
 5. The covering material for solar thermal power generationsystem according to claim 4, wherein the film having a cable attached toits end, is a film obtained by folding back the peripheral portion ofthe film to enclose the cable and thermally fusion-bonding the surfacesat the folded-back peripheral portion.
 6. The covering material forsolar thermal power generation system according to claim 5, wherein thesurfaces to be thermally fusion-bonded are non-hydrophilic treatedsurfaces.
 7. A solar thermal power generation system formed by spreadingthe covering material for solar thermal power generation system asdefined in claim 1 is stretched.